The present invention relates to a pneumatic tire provided in the sidewall portion with a white rubber layer, more particularly to an improved tire sidewall structure being capable of preventing the white rubber form change of color due to adjacent black rubber.
In the pneumatic tires for motorcycles, passenger cars and the like provided in the sidewall portions with white veneer rubber, a part of the white rubber adjacent to black rubber is liable to change color because chemicals, e.g. antidegradant and the like spreads from the black rubber to the white rubber as time go by. Therefore, if the white veneer rubber on the black rubber is thin, the whole of the white rubber becomes dirty. If the thickness of the white veneer rubber is increased, this may be avoided, but the durability and steering stability are liable to deteriorate because the white rubber generally has a lower rigidity and a lower strength than the black rubber.
In case of motorcycle tires, in comparison with tires in other categories such as passenger car tire and the like, the sidewall portion becomes relatively small because the tread portion is curved with a relatively small radius of curvature and accordingly approaches the bead portion. As a result, the occupation of the white veneer rubber in the sidewall portion increases, and the durability and steering stability decreases since the deformation of the sidewall portion is especially larger during cornering. Thus it is difficult to increase the occupation of the white veneer rubber on the black rubber without deteriorating the durability, steering stability and the like.
It is therefore, an object of the present invention to provide a pneumatic tire, in which a white rubber layer disposed in the sidewall portion can be prevented from change of color without decreasing the durability steering stability and the like.
According to the present invention, a pneumatic tire comprises
a tread rubber layer (2) disposed radially outside a carcass (6) to define a part of the tire outer surface between tread edges (P1),
a side rubber layer (V) disposed axially outside the carcass (6) to define a part of the tire outer surface radially inward of each tread edge (P1), the side rubber layer (V) comprising a radially outer black sidewall rubber (15), a radially inner black sidewall rubber (16) and a white sidewall rubber (14) therebetween,
a wing rubber layer (12) interposed between the tread rubber layer (2) and the side rubber layer (V),
the surface of the wing rubber layer (12) consisting of a part (12a) contacting with the carcass (6), a part (12b) contacting with the tread rubber layer (2), and a part (12c) contacting with the radially outer black sidewall rubber (15) and the white sidewall rubber (14), and
the surface of the radially outer black sidewall rubber (15) consisting of a part (15c) extending form the tread edge (P1) to a point (P3) on the tire outer surface, a part (15a) contacting with the wing rubber layer (12) and extending from the tread edge (P1) to a point (P2), and a part (15b) contacting with the white sidewall rubber (14) and extending from the point (P2) to the point (P3),
the radially inner black sidewall rubber (16) extending radially inwardly from a point (P4) on the tire outer surface radially inside the point (P3) while contacting with the axially outside of the white sidewall rubber (14),
the white sidewall rubber (14) provided between the point (P3) and the point (P4) with a protruding part (17) so that the thickness (DP) of the white sidewall rubber (14) in the protruding part (17) measured from the outer surface to cords of the carcass is not less than 4 mm, and
the thickness (DS) of the radially outer black sidewall rubber (15) having a maximum value of not less than 3 mm at the point (P2).